1. Field of the Invention
This invention concerns an impeller used in the field of fluid transfer using rotating machinery. The invention more particularly concerns an impeller specifically developed for use with corrosive fluids while maintaining standard performance characteristics.
2. Discussion of the Background
Traditional impellers employ blades to transfer the fluid from an inlet, or suction eye, through the interior of the impeller and then discharged through an outlet. The blades of the impeller can be oriented relative to the axis of rotation of the impeller in a radial direction, a forwardly inclined direction, or a backwardly inclined direction. The forwardly inclined blade design employs a blade which has an exit edge which is forward of the inlet edge of the blade relative to the direction of rotation of the impeller. For example, relative to a fixed rectangular coordinate system located at the axis of rotation of the impeller, but not fixed to the impeller, the exit edge of the blade crosses any one of the coordinate axes before the inlet edge of the blade crosses the corresponding coordinate axis when the impeller is rotated. Likewise, the backwardly inclined blade design employs a blade which has an inlet edge forward of the exit edge of the blade relative to the direction of rotation of the impeller. The backwardly inclined blade design is more efficient than either the radial or forwardly inclined blade designs.
However, backwardly inclined blade designs have a major drawback over the other two types of blade orientation in that the blade stresses are much greater. The larger stresses have tended to require that the material of construction of the blades be restricted to steel due to its high strength, stiffness, and fatigue characteristics. As such, the steel blades allow for blade angles and contours which maintain good flow characteristics and performance characteristic.
The steel blades are adequate for many uses and environments. However, when steel impellers are employed to transmit corrosive materials, the steel impellers corrode. The steel impellers employed to transmit the corrosive fluids work satisfactorily for a short period of time before the corrosive effect of the working fluid corrodes the steel impeller to the point of uselessness. To overcome the problem of corrosion to the material of the impeller, fiberglass reinforced plastic has been employed since fiberglass reinforced plastic has superior corrosion resistant properties as compared to steel.
However, the large stresses mentioned earlier require that either the thickness of the blades be increased or the angle of inclination be compromised. Furthermore, increasing the thickness of the blades increases the mass moment of inertia of the impeller thus requiring increased operational power, limits the number of blades that can be placed on the impeller, and adversely affects blade aerodynamics.